PROJECT SUMMARY Preterm birth ? delivery at less than 37 weeks gestation ? is a significant global public health challenge, and preterm rates in the United States are considerably higher than they were several decades ago. Explanations for these increases remain elusive, and environmental risk factors are an understudied but potentially important area for discovery of modifiable risk factors and high-impact interventions. Compared to the United States overall, significantly higher rates of preterm birth exist in Puerto Rico, where nearly 12% of all births are preterm. Rates of other adverse pregnancy outcomes are also much higher in Puerto Rico than in the US, and Puerto Rico has a large number of Superfund and other hazardous waste sites, and additional factors that may result in elevated exposures to environmental pollution, such as hurricanes, flooding, and other events. This project proposes to continue our prospective cohort study of novel risk factors for preterm birth and other adverse pregnancy outcomes, with a focus on exposure to mixtures of Superfund-relevant chemicals. We propose to expand our cohort to include 2,000 live births in northern Puerto Rico with detailed information and samples collected at multiple times during pregnancy. We will then utilize state-of-the-art methods to estimate biomarkers of exposure to chemical mixtures, in addition to intermediate biomarkers of effect in order to provide much needed human data on environmental and other predictors of pregnancy outcomes in Puerto Rico, and insights on the biological pathways involved. Results from our study thus far suggest that oxidative stress may be an important link between exposure and outcome that needs to be explored in more depth. The study aims to develop and incorporate innovative statistical techniques for mixtures and mediation, and identify conditions and activities contributing to high exposures that can inform effective exposure reduction strategies. Our specific aims are to: 1) Investigate exposure to a range of Superfund-relevant chemicals (phthalates, polycyclic aromatic hydrocarbons [PAHs], and metals, both as individual chemicals and as mixtures) and adverse pregnancy outcomes, including preterm birth, impaired fetal growth (using data from repeat ultrasound scans), birth weight, preeclampsia, and gestational diabetes; 2) Determine demographic, geographic, behavioral, weather, and other factors associated with higher exposure biomarker concentrations, both for individual chemicals and multiple chemicals concurrently to inform exposure and risk reduction efforts; and 3) Utilize state-of-the-art biomarkers and innovative statistical methods to discover oxidative stress pathways involved in the relationships between chemical exposures and adverse pregnancy outcomes. The expected outcomes of this study are new and much needed information on the magnitude, sources, and impacts of exposure to Superfund-related chemicals, both individually and in combination, among pregnant women in this high-risk population, and innovative methods for identifying relevant biological pathways and assessing health impacts from exposure to mixtures. Our findings are likely to have a significant positive impact on public health.